This invention relates to an adhesive based on an aqueous polymer dispersion containing added thickeners and optionally fillers, pigments, preservatives, solvents, plasticizers and other auxiliaries. The invention also relates to its production and to its use as an assembly adhesive.
An assembly adhesive is understood to be a composition which, on the strength of the following properties, is suitable for assembly purposes above all in the building industry:
very high early strength and ultimate strength in the bonding of wood, metals, ceramics, PVC and other plastics both indoors and outdoors and particular abilities in regard to
gap bridging,
adhesion spectrum and
flexibility.
A preferred application for assembly adhesives is the rapid and permanent fixing of objects to ceilings, walls and floors. A particular requirement in this regard is the rapid and simple assembly of heavy objects without any need for additional fixing after application of the adhesive (for example in the bonding of bricks, clinker bricks, panels, ceiling boards, etc.). The adhesive composition also has to be capable of xe2x80x9cbridgingxe2x80x9d any surface unevenness (gap bridging).
The assembly adhesives hitherto available on the market have a maximum early strength of 10 g/cmxe2x88x922 so that, although light objects can be assembled without any need for additional fixing, problems do arise in the case of heavy objects, such as ceiling panels for example. Further problems arise in the assembly of items which are under tension (for example curved skirting boards). Items such as these have to be additionally fixed until the adhesive has cured. Assembly applications such as these always involve time-consuming and, in some cases, complicated extra work.
There are four types of assembly adhesives:
a) solvent-containing systems,
b) reactive systems,
c) hotmelt adhesives,
d) water-based systems.
Solvent-containing assembly adhesives are unpopular, particularly for indoor work involving large surface areas, because troublesome odor emission is often caused by solvent vapours. The advantage of using solvent-containing systems is that the solvent present is able to escape quickly from the adhesive composition so that high early strength can be obtained relatively quickly for assembly jobs.
Reactive systems and hotmelts either require special conditions/equipment for application or take a relatively long time to develop adequate adhesion properties for assembly work.
Water-based systems have the disadvantage that the water present is released very slowly. Accordingly, the curing process of the adhesive is relatively slow. The major advantage of water-based systems is that there is no odor emission and/or health risk from solvent vapours. However, there have hitherto been no assembly adhesives with adhesion values in excess of 10 and more particularly in excess of 15 g/cmxe2x88x922.
Where acrylate dispersions are heavily thickened with relatively high concentrations of acrylate thickeners to achieve high early strength (particularly via their viscosity), it has hitherto only been possible to obtain very high-viscosity adhesive compositions that are difficult to apply, are not stable in storage and show poor wetting behavior on the substrates to be bonded.
GB 2 061 990 describes an adhesive for fixing ceramic tiles. It contains
2 to 50% by weight of an aqueous dispersion or solution of an organic polymer with a solids content of 30 to 70%,
4 to 80% by weight of an inorganic filler,
0.5 to 15% by weight of an organic additives and
0 to 10% by weight of auxiliaries.
In the Examples, adhesives are made up from the following components:
100 parts by weight of a styrene/acrylate copolymer in the form of a dispersion with a solids content of 45%,
450 parts by weight of sand with various particle sizes,
5 parts by weight of a coalescence solvent based on an aromatic glycol ether,
1 to 2 parts by weight of cellulose ether with a viscosity of 15,000 as thickener,
2 to 1 part by weight of Aerosil and
50 to 55 parts by weight of water.
Besides cellulose ethers, polyacrylates are mentioned as organic thickeners. The adhesive in question is said to be used for fixing ceramic tiles to floors. Apparently, however, ceramic tiles can even be fixed to walls. The disadvantage of this known adhesive is that its early strength is not high enough for fixing heavy items, such as tiles for example, to walls immediately after levelling of the adhesive.
The problem addressed by the present invention was to provide a storable adhesive with very high early strength for fixing heavy items. The adhesive would be easy to use. This would apply in particular to its application to and spreading over the substrate.